Could I be pregnant even though I have the implant?

I got nexplanon in December 2014 so it's my second year. A few months ago I was constantly bleeding so my doctor gave me some birth control pills to help build up my uterine wall and it did help pretty well and I haven't had a period for like about a month. I'm scared I might be pregnant because my nipples are really sore and usually my breasts just get sore not the nipple part. I've never been pregnant so I don't know symptoms but I looked it up. Can it just be that they're just pms symptoms?